**Al-Cr-Ti-N**

Various quaternary cubic (AlCrTi)N coatings with a composition of about (Al60(Cr,Ti)40)N and varying Ti content (0, 1, 2, 11 at.%) were deposited by cathodic arc evaporation. The hardness of the (Al30.5Cr14 Ti5.5N50) coating was retained after annealing up to 1100 ◦C. The coating also showed an age hardening process caused by spinodal decomposition similar to (AlTi)N [97]. However, the oxidation resistance was found to be slightly reduced compared to unalloyed (AlCr)N coatings. The age hardening effect was also discussed for AlCrTiN coatings with a higher Al content (Al66Cr24Ti10)N [98]. It was shown that the oxidation resistance of (Al69Cr20Ti11)N was significantly increased as compared to (Ti50Al50)N [99].
